Curing mechanisms with epoxy resins

The curing mechanism of epoxy resins with carboxylic hydrazides has not been sufficiently revealed so far. However, Kamon 36) has shown that one hydrazide group reacts with two epoxy groups. This result suggests that the structure of the epoxy resin cured with hydrazide is presumed to be nearly the same as that shown in Fig. 1 a, where the — NC segment is substituted by the -CONHN segment. 

The curing mechanism of epoxy resins with imidazol was investigated. The following mecha-... 

Crosslinkers generally used to cure and modify the properties of alkyd/polyester resins include amino resins, phenolic resins, polyisocyanates, epoxy resins, silicone resins and vinyl monomers. In this section, the curing mechanism with amino resins and vinyl monomers will be mainly discussed. Also, the importance and influence of such curing reactions on paint performance will be briefly summarized. However, no attempt will be made here to review the structural influence of basic components in the resins on paint performance. This has recently been comprehensively reviewed. ... 

The early reaction mechanism of DICY with epoxy resin consists of the epoxy reaction with all four hydrogen atoms on DICY and the epoxy-to-epoxy reaction that is catalyzed by the tertiary amines. The final curing mechanism is between hydroxyl groups in the partly cured resins and DICY cyano groups. This results in the disappearance of the cyano groups to form amino groups. This step is also catalyzed by tertiary amines. 

Among these hardeners, amines are the most versatile ones at room temperature as well as elevated curing temperature. The curing mechanisms with amines and the structures of the amine cured epoxy resins have been most sufficiently studied, and the systems of epoxy resins with amine hardeners are most extensively used in the practical industrial fields. 

The reaction mechanism of liquid dimer polyamides and fatty amido amines with epoxy resins has been studied by Peerman et al. (27). who employed infrared spectroscopic analysis to determine reaction rates. They showed that the terminal epoxy content of a blend of amino-containing polyamide and epoxy resin disappeared more rapidly at 150 °C than does the epoxy content of blends of epoxy resin with triethylenetetramine or tris[(dimethylamino)-raethy1Jphenol. Both of these compounds are well-known for their fast cure at ambient temperatures. Correspondingly, the liquid polyamide or fatty amido amines-epoxy combinations cure slower than the other two systems at ambient conditions. 

Three different types of curing mechanism can be distinguished Primary and secondary amines react with epoxy resins by an addition mechanism. 

Figure 3.4 Anhydride-curing mechanism for epoxies (a) reaction of hydroxyl group (from epoxy resin) with anhydride (b) reaction of carboxylic acid group with epoxy (c) reaction of...

Epoxy composites cured with IPD offer resistance to a wide range of chemicals up to about 100-120°C. They offer better corrosion resistance in general than polyesters, but in many respects they are not quite as good as epoxy vinyl esters. This is due to the presence in the cured resins of the more sensitive amine hardeners. They nevertheless outperform other resins in their resistance to water at temperatures above about 80°C. Because of the excellent mechanical properties associated with epoxy resins, they are the system of choice when high pressure pipes are required. 

Impetus (52) for study of IPNs of epoxy and unsaturated polyester results from the lower cost and good performance possible when unsaturated polyester is mixed with epoxy resin. Since polyesters cure by a free radical mechanism, and epoxies cure by cationic initiation followed by condensation, it would appear to be possible to cure the polyester and the epoxy independently of one another. However, this does not seem to be the case. When concentrations are chosen so that the IPN has equal parts of each component, there is an unusually rapid... 

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